Add require option to Gemfile
Add require option to Gemfile

If you're using Rails, or anything else that calls `Bundler.require`, you need this option to have things work correctly (otherwise, bundler will try to require `'mailgun-ruby'`).
travelton/mailgun-ruby,mailgun/mailgun-ruby,pirogoeth/mailgun-ruby,veracross/mailgun-ruby,brightcommerce/mailgun-ruby